Method for investigating the thrombocyte function of the blood

ABSTRACT

The invention relates to a method for investigating the thrombocyte function of the blood, wherein the following steps are carried out: a) cross-flowing an aperture ( 3 ) with blood or blood components; b) determining the active radius of the aperture ( 3 ) depending on time and c) evaluating the time-dependent modification of the radius as a measure for blood cell and/or thrombocyte function.

The invention at hand has to do with a technique and a mechanism fortesting the thrombocyte function in blood.

There are various mechanisms for testing the aggregation of bloodplatelets or the coagulation of blood. For example, a mechanism is basedon the EP 0223044 B1 in which the blood is aspirated through an apertureout from a blood supply space by means of a moveable piston in acylinder and the pressure in the space between the piston and theaspirated in blood is measured, whereby the piston is driven in such away that a target pressure value is maintained in the space. The pistonmovement serves as a measurement for the amount of blood flow.

The role of the invention at hand consists in creating a technique and amechanism that enable to get an exact determination of the thrombocytefunction in the blood.

This role is performed by a technique with the features of the patentclaim 1 and a mechanism for carrying out this technique.

The essential advantage of the invention at hand consists in allowingfor an exact determination of the blood platelet delay time by means ofwhich the arterial thrombus growth is controlled or influenced. Thus,since in accordance with the invention it becomes possible to measurethe designated blood platelets' delay time, for the first time evidencecan be gathered on e.g. existing disease risks, such as arterialthrombotic tendency, for example the risk of myocardial infarction in apatient. For the first time medications can be developed thatselectively have an effect on the blood platelet delay time to eliminatesuch risks.

The determination of the blood platelet delay time in a patient's freshblood so to speak ‘bedside’ very quickly (without blood thinners) and ona very small volume of blood can be arrived at by means of a specialdesign of the invention-related mechanism.

With a particularly preferred design of the invention the thrombocytefunction can be determined at a very high degree of reproducibility andpreciseness fast and with only a little volume of blood.

Advantageous designs for the inventions are derived from the subclaims.

Below the invention and its designs will be explained in more detail inconnection with the figures. Shown are:

FIG. 1 a mechanism for determining the blood platelet delay time inschematic representation;

FIG. 2 a diagram for demonstrating the relationship of the aperturediameter to the time, caused due to occlusion by the blood platelets;

FIG. 3 a diagram for demonstrating the wall shear rate as a function oftime;

FIG. 4 a mechanism designed as a disposable part for implementing theinvention-related technique in schematic representation; and

FIGS. 5 and 6 preferred designs of the invention.

The following considerations and realizations led to the inventions. Atime-dependent determination of the loading of an aperture by means ofblood platelets when flowing through it surprisingly revealed that theaperture closes in a completely defined way, that is in accordance withthe straight line depicted in FIG. 2, whose slant 2 dr/dt yields thegrowth rate. When simultaneously calculating the blood platelets'time-dependent wall shear rate that represents a measurement for bloodplatelets' transport rate, it was recognized that in time the wall shearrate sharply rises from a low value at first in the area of theaperture. But since the growth rate during this time remains exactly thesame, it can be inferred that a blood platelet delay time exists thatindicates that time over which the individual blood platelets firstallow an adhesion of other blood platelets. In other words each bloodplatelet “determines” when, i.e. thus after which lag in time or delaytime, other platelets may adhere to it. This blood platelet delay timein connection with certain disease risks and with the development ofmedications is of primary importance. This means that by theinvention-related finding of the mentioned rise dr/dt, i.e. thereforethe blood platelet delay time, selective evidence on disease risks, e.g.on the risk for myocardial infarction in a patient, can be gathered andfor this reason medications can be selectively developed that influencethe blood platelet delay time.

FIG. 1 shows an existing mechanism for determining the blood plateletdelay time in schematic representation. In essence here according toarrow 1 blood is moved out of a supply space that is not described inany greater detail, for instance via a capillary 4 that forms a bloodflow resistance stream Wc, through an aperture 3 of an aperture holder2. The aperture 3 forms a blood flow resistance Wa.

According to the following equation $\begin{matrix}{{{Wa} = \frac{\Delta\quad P}{Q}}\left( {Q = {{volume}\quad{of}\quad{blood}\quad{flow}\quad{per}\quad{time}}} \right)} & (1)\end{matrix}$as well as according to the Hagen-Poiseuille law $\begin{matrix}{{Wa} = {\frac{8\mu\quad l}{\pi} \cdot \frac{1}{r^{4}}}} & (2)\end{matrix}$by time-dependent calculation of the resistance Wa the effectivehemodynamic radius of the aperture 3 in accordance with the equation$\begin{matrix}{r = \sqrt{\frac{8\mu\quad l}{\pi} \cdot \frac{1}{Wa}}} & (3)\end{matrix}$can be calculated and spread over time in accordance with FIG. 2.

In equations 1 through 3:

-   -   Δp designates the drop in pressure at the aperture, Wa the flow        resistance of the aperture, μ the viscosity of the blood flowing        through the aperture, 1 the gauge of the aperture and r the        radius of the same.

In FIG. 2 it can be seen that the opening of the aperture 3 quitedefinitely closes as a function of time surprisingly in accordance witha straight line with a constant slope of (dr/dt=const) with a very highvalue of statistical probability: e.g. RSq=0.982. If a platelet diameterof 2 μm is assumed,

-   -   a platelet delay time of 2/0.7=2.8 sec is obtained. With a first        control person with normal platelet function a platelet delay        time of 2.77+0.32 sec. was determined. The number of        measurements was 11. With a second control person the platelet        delay time amounted to 2.65+0.1 sec. with 11 measurements and a        normal platelet function as well.

Instead of the drop in pressure Δp at the aperture 3 the drop inpressure Δp′ can be measured at the capillary 4 and the aperture 3,whereby then the capillary 4 flow resistance Wc has to be deducted todetermine the growth rate.

According to the formula: $\begin{matrix}{{\gamma\quad w} = \frac{4Q}{\pi\quad r^{3}}} & (4)\end{matrix}$the wall shear rate γω in the area of the aperture can be calculated andspread in a time-dependent fashion like FIG. 3. The result is that theplatelets' transport rate on the thrombus that is approximatelyproportional to the wall shear rate rises during the measuring by thefactor 4. During this rise though, just as in FIG. 2, the thrombusgrowth rate remains exactly the same. The inference is that theindividual blood platelets in the area of the aperture 3 determine inaccordance with a platelet delay time when other blood platelets mayadhere to them. The blood platelet delay time, therefore, matches thetime difference between a blood platelet's adhesion on the wall of theaperture 3 or on another blood platelet and the adhering of anadditional blood platelet.

FIG. 4 illustrates a design of the mechanism at hand in schematicrepresentation, wherein blood from a blood supply space 10 is pressed orconveyed with the assistance of a piston 12 through the aperture 3 intoa blood collecting space 14. The blood supply 10 is preferably designedin a cylinder 16 in which the piston 12 is arranged pushable. Thepiston/cylinder arrangement 12, 16 can for this purpose have the shapeof a blood withdrawal syringe, wherein the blood supply space 10 isfilled when withdrawing blood from a patient's vein. After removing thewithdrawal cannula the forward end 18 of the piston/cylinder arrangement12,16 can be connected with the section encompassing the bloodcollection space 14 that is preferably designed as a disposable orsingle use section, wherein the part of its access opening 20 that isconnectable to the piston/cylinder arrangement 12, 16 has an apertureholder 22 with the aperture 3 down stream, through which the bloodtraverses from the blood supply space 10 into the blood collecting space14 upon activation of the piston 12 in the direction of the arrow 24.

A capillary (in FIG. 1: reference symbol 4) can be placed upstream toaperture 3, as is already familiar.

To measure the pressure reduction on the aperture 3, the disposablesection can have a passage 26 that is connected to a pressure metermechanism in a gauge when taking readings and that runs inside or alongits wall from outside to the space upstream of aperture 3.

One advantage here is that after withdrawing blood, for instance at thepatient's bed, the disposable section for carrying out the technique athand can be connected directly to the piston/cylinder arrangement 12, 16that serves for withdrawal of blood and along with the piston/cylinderarrangement 12, 16 put into the gauge that implements the technique athand and activates the piston 12.

It should be pointed out that for measuring with a small volume of blood(e.g. in pediatrics) it can be advantageous when carrying out thetechnique at hand not to activate the piston 12 continuously, but ratherjerkily,

-   -   whereby, for example, the movement of the piston 12 is        interrupted at intervals that could be on the order of 3        seconds.

Only one segment of the straight-line dr/dt in FIG. 2 can also bemeasured, e.g. for measuring with little blood, whereby thecorresponding bleeding time can be determined by extrapolating.

Since it is known that a straight-line is to be determined, measurementswith stark deviations can be recognized as erroneous and corrected byextrapolating in the areas of deviation. Furthermore, it can also besufficient to determine only a segment of the straight-line and not todetermine measured areas by extrapolating. For example, this can becarried out to save time.

Since the platelet delay time is not dependent on the capillaryresistance in the case of using a capillary, capillary errors do notenter into the measurement, thus the measurement precision andreliability can be enhanced.

Below a variation on the invention-related technique is explained inmore detail in connection with FIG. 5, by which is possible aparticularly advantageous and clear and significant assessment for theuser or measurement of the thrombocyte function with a relatively smallvolume of blood, with short measuring times and an even greaterreproducibility.

These advantages are achieved due to the fact that by this variation theslope of the straight-lines dr/dt is indeed determined, yet no value CTof the bleeding time is extrapolated, but rather the PTGA angle(Platelet Thrombus Growth Angle) that exists between the straight-lineand the t-axis (see FIG. 5). This is particularly advantageous if thisangle is relatively small and the straight-line for this reason runsflat, as is the case with a very slow thrombus formation in the aperture3 which applies e.g. to a-taking of medication (for example, aspirin) Inthis case enormous fluctuations in the CT value would result by thetechnique explained above even with small deviations of the slope dr/dtof the straight-line. These fluctuations are all the greater the fartherthe CT value is removed from the t-axis zero point. In such a case thedetermination or indication PTGA angle is more significant since it isnot subjected to the designated fluctuation. Furthermore, this PTGAangle can be derived very fast from the straight-line's slope determinedat the start of a measurement by the formula indicated below, thus themeasuring time can be relatively short and an only relatively smallvolume of blood is needed for measuring.PTGA=−(((arc Tan(dr/dt))/(n/2))90)   (5)

Determined.

Accordingly even the PTGA′ angle can be determined by the formula:PTGA′=90−PTGA   (6)and applied.

The thrombocyte function can, as already mentioned, be quicklyestablished by this variation of the invention at hand, i.e. even with asmall volume of blood, particularly also with relatively long thrombusformation times in the aperture 3, as this is possible, for example,with influences of medications, e.g. with the taking of aspirin. Herethe values of the PTGA or PTGA′ angles determined are to a certainextent comparatively significant because they are not subjected to suchgreat fluctuations as the CT values determined.

A still more improved measurement is made possible with an additionalvariation of the technique at hand, according to which a fit operationis performed to compensate for changes in blood viscosity and/or theresistance Wc of capillary 4 (FIG. 1). Here with a value t=0 the startvalue of the aperture opening is always set or fitted to apre-established defined value V (from e.g. 150 μm in the FIGS. 2 and 5)in such a way that the straight-line at the beginning of a measurementis calculated by extrapolating up to the zero point of the t-axis andthe value thereby determined for t=0 shifted to the per-establishedvalue V. Proceeding from this value V then the straight-line isdetermined and the CT value according to FIG. 2 or the PTGA or PTGA′angle according to FIG. 5. In this way the measurement data can befurther enhanced because fluctuations in viscosity or the capillaryresistance are compensated.

Below an additional variation of the technique at hand is explained bywhich a quality control of the determined straight-line or thedetermined PTGA or PTGA′ angle is effected. In so doing, as indicatedearlier above, it is determined how precisely the measured values dr/dtline on a straight-line or not. With deviations of a pre-establishednumber of values beyond a prescribed measure the correspondingmeasurement is deemed not processable or corrected.

With certain disease condition or under the influence of medicationthere may be deviations from the linear relation dr/dt. For example, inthe FIG. 2 by means of a pointed line is depicted that the slope of thestraight-line during a measurement can change in such a way thestraight-line can encompass two segments of varying slopes dr1/dt anddr2/dt, whereby the point of intersection P of these segments is to beascribed for a certain thrombus formation that is established by certaindisease pattern. In such cases the point P is very significant for whichreason it is determined with the measurement.

Below an additional preferred form of implementation of the technique athand is explained in more detail. This essentially has a piston/cylinderarrangement 10 that encompasses a cylinder 30 and a piston 50. Thepiston 50 can be moved in the direction of the arrow 70, i.e. thereforein its axial direction in the cylinder 30 by means of drive that is notillustrated in any more detail.

The piston 50 preferably has the shape of a metal part polished on itsouter surface that consists in particular of stainless steel andpossesses the shape of a lengthwise cylindrical rod section. Between theouter surface of the piston 50 and the inner surface of the cylinder 30that also preferably consists of stainless steel is arranged an 0-ringgasket 90 that preferably consists of a rubber material. Since the outersurface of the piston 50 is polished between the gasket 90 and thepiston 50 there is extremely little friction so that a jerk-freemovement of the piston 50 in the direction of the arrow 70 is assured.

With its end away from the drive that is not illustrated in more detailthe piston 50 extends out into a blood uptake space 1 10 that isestablished by means of a beaker-shaped vessel 130 that is positionedtightly up against the cylinder 30 with its upper edge area adjacent tothe piston 50 with the aid of a gasket 150. For this reason the cylinder30 has a flange section 170 that extends radially outwards and on theupper edge of the vessel 130 a flange section 190 that protrudes towardthe outside radially as well, whereby the O-ring gasket 150 is keptbetween the flange section 170 and 190 and connects the latter tightlyto each other. On the bottom 210 of the vessel 130 an aperture holder230 is located that holds a platelet 250 or the like with an aperture270 arranged in it, whereby a capillary 290 led from outside through thebottom part 210 in an inherently familiar way ends shortly prior to theaperture 270 in such a way that out of a blood supply space (not shown)blood that has been aspirated in through the capillary 290 with themovement of the piston 50 in the direction of the arrow 70 is taken inthrough the aperture 270 into the uptake space 110. The aperture 270 canalso be designed and arranged in another way. For example, the end ofthe capillary 290 that protrudes through into the uptake space 11 canform it.

One pressure-measuring mechanism P that is not illustrated in greaterdetail is connected to a passageway 310 preferably in the wall of thecylinder 30 for measuring the pressure outside of the blood that hasbeen aspirated through the aperture 270 into the uptake space 110. Inthis way it is achieved that the vessel 130 is fastened to the apertureholder 230 and the capillary 290 and can be designed as a so-calleddisposable part and via the gasket 150 optionally to the piston/cylinderarrangement 11 in the simplest way.

It should be pointed out that instead of determining the drop inpressure at the aperture 3 an electrical resistance also could beestablished by application of a potential difference for determining thehemodynamic resistance of the aperture 3. The radius of the aperture 3that just exists can also be optically determined.

1. Technique for testing the thrombocyte function in blood, whereby anaperture (3) with blood or blood components is flowed through, thuscharacterized that the following steps below are performed: a)Determining the effective radius of the aperture (3) as a function oftime by measuring the drop in pressure at the aperture (3) as a functionof time and determining the blood flow volume through the aperture (3)as a function of time. b) Calculation of the hemodynamically effectiveradius of the aperture (3) by the Hagen-Poiseuille law. c) Evaluation ofthe time-dependent change in the radius as a measure for the blood celland/or thrombocyte function.
 2. Technique according to claim 1, thuscharacterized that assuming a Prescribed blood platelet diameter theplatelet delay time is established from the slope (dr/dt) of thedetermined straight-line and the blood platelet as a measure for thethrombocyte function.
 3. Technique according to claim 1, thuscharacterized that a value (CT) is determined, in which the aperture (3)is closed by blood cell or thrombus formation up to a given measure, asthe measure for the thrombocyte from the determined straight-line. 4.Technique according to claim 1, thus characterized that the value (CT)is pre-established for a radius of the value zero.
 5. Techniqueaccording to claim 1, thus characterized that an angle (PTGA) existingbetween the determined straight-line and the axis for time (t) isestablished as a measure for the thrombocyte function.
 6. Techniqueaccording to claim 1, thus characterized that an angle PGTA′) that theetermined straight-line and the axis for the radius (r) is establishedas a measure for the thrombocyte function.
 7. Technique according toclaim 1, thus characterized that the value of one selected section ofthe straight-line is determined by measurement, and at least one othersection of the straight-line is determined by extrapolating on the basisof the selected straight-line.
 8. Technique according to claim 7, thuscharacterized that the value of the straight-line at the point in timezero (t=0) is determined and the straight-line is shifted by changingparameters in the Hagen-Poiseuille law in such a way that the value ofthe radius (r) at the point in time zero (t=0) corresponds to apre-established value (V).
 9. Technique according to claim 1, thuscharacterized that the point of intersection (P) of two or more segmentsof varying slopes (dr1/dt; dr2/dt) of straight-lines determined during ameasurement is determined as a measure for certain processes in thrombusformation.
 10. Technique according to claim 1, thus characterized thatthe correlation of measuring points is calculated with a mathematicalfunction, preferably a straight-line, for the quality control of ameasurement.
 11. Mechanism, in particular for implementing the techniqueaccording to claim 1, thus characterized that a blood supply space (110)is foreseen, from which blood is conveyable via an aperture (270)through a iston/cylinder arrangement (10), whereby the aperture (270) isarranged in a platelet (250) that is kept on the side of a bottom wall(210) by an aperture holder (230) turned toward the uptake space (110)in a vessel (130) that form the blood uptake space (110).
 12. Mechanismaccording to claim 11, thus characterized that a capillary (290) Runsfrom the outside of the vessel (130) through the bottom wall (210) ofthe same to just shortly before the aperture (270).
 13. Mechanismaccording to claim 11, thus characterized that the open side of thevessel (130) turned toward the piston/cylinder arrangement (10) isconnectable via a gasket (150) tightly to the end of the piston/cylinderarrangement (10) that is turned toward the vessel (130).
 14. Mechanismaccording to claim 13, thus characterized that the cylinder (30) of thepiston/cylinder arrangement (10) has a flange section pointed outwardsradially on its side toward the vessel (130), so that the vessel (130)has a flange section (190) protruding out radially toward the outside onits side turned toward the piston/cylinder arrangement (10) and that anO-ring gasket (150) is arrangeable for sealing the connection of thevessel (130) to the piston/cylinder arrangement (10) between the flangesection (170) of the cylinder (30) and the flange section (190) of thevessel (30).
 15. Mechanism according to claim 11, thus characterizedthat the piston (50) of the piston/cylinder unit (10) has the shape of acylindrical metal rod section.
 16. Mechanism according to claim 15, thuscharacterized that the rod section Forming the piston (50) is highlypolished on its outer surface.
 17. Mechanism according to claim 15, thuscharacterized that the rod section consists of steel.
 18. Mechanismaccording to claim 15, thus characterized that between the rod sectionforming the piston (50) and the cylinder (3) an O-ring gasket (90)arranged.
 19. Mechanism according to claim 11, thus characterized thatthe end area of the piston (50) protruding into the vessel (110) to alarge extent fills up the volume of the vessel (110) in order to avoiddamaging dead spaces when aspirating blood through the aperture (270).20. Mechanism according to claim 11, thus characterized that the vessel,the aperture holder (230) and as the case may be the capillary (290) aredesigned as a disposable part (130).
 21. Mechanism in particular forcarrying out the technique according to claim 1, thus characterized thatit has a supply space (10) that through the aperture (3) is connectablevia one section's access opening (20) to a blood gathering space (14)formed in the section.
 22. Mechanism according to claim 21, thuscharacterized that the supply space (10) is formed in a cylinder (16) inwhich a piston (12) for conveying blood through the access opening (20)into the blood gathering space (14) and is arranged relocatable throughthe aperture (3).
 23. Mechanism according to claim 22, thuscharacterized that the cylinder (16) and the piston (12) are formed by ablood withdrawal syringe the forward end of which is connectable to theaccess opening (20) after removal of a withdrawal cannula.
 24. Mechanismaccording to claim 22, thus characterized that the section has anAperture holder (22) with the aperture (3) that is downstream of theaccess opening (20).
 25. Mechanism according to claim 21, thuscharacterized that the section is designed as a disposable part. 26.Mechanism according claim 21, thus characterized that the section has apassage (26) running along its was from outside to a space upstream ofthe aperture (3) that is connectable to a pressure measuring device formeasuring pressure.
 27. Mechanism according to claim 21, thuscharacterized that a capillary is upstream of the aperture (3). 28.Mechanism according to claim 27, thus characterized that the capillaryis a component of the disposable part.